The infamous hacker claims he broke into Hillary Clinton's personal e-mail server. In the meantime, the presidential hopeful is under criminal investigation for using the server to handle classified information.

Then-Secretary of State Hillary Rodham Clinton checks her Blackberry from a desk inside a C-17 military plane in 2011. Infamous Romanian hacker Marcel Lazar says that he hacked e-mails stored on her private server.

The infamous Romanian hacker, whose cyber exploits are connected to exposing Hillary Clinton’s potentially illegal use of private e-mail to conduct business when she was secretary of state, now has said that he hacked her e-mails, stored on her private, "completely unsecured" server.

In an NBC News interview from jail in Bucharest, 44-year-old Marcel Lazar, a former taxi driver and paint salesman from rural Romania, said of Mrs. Clinton’s e-mails, "it was like an open orchid on the Internet."

"There were hundreds of folders," said Mr. Lazar, also known as “Guccifer.”

“There is absolutely no basis to believe the claims made by this criminal from his prison cell,” Clinton campaign spokesman Brian Fallon said.

“In addition to the fact he offers no proof to support his claims, his descriptions of Secretary Clinton’s server are inaccurate. It is unfathomable that he would have gained access to her emails and not leaked them the way he did to his other victims,” said Mr. Fallon, according to Politico.

Since the interview with NBC, which is due to air Sunday, Lazar has been extradited to the United States to face charges of wire fraud, aggravated identity theft, cyberstalking, and obstruction of justice, according to Reuters. He's suspected of hacking into the e-mail accounts of a number of high-profile political figures and is awaiting trial in September.

Guccifer already had claimed responsibility in 2013 for hacking the e-mails of Bush family members, reports Reuters, and for posting George W. Bush’s stolen artwork online, including a self portrait in the bathtub.

He also made public e-mails exchanged by former US Secretary of State Colin Powell and Corina Cretu, a Romanian member of the European Parliament, reports Reuters. This prompted retired Gen. Powell to deny that the two had an affair.

Guccifer also took credit in 2013 for hacking the AOL account of Sidney Blumenthal, who was an adviser to former President Bill Clinton, and who “frequently traded back-channel intelligence, diplomatic messages and political gossip with Hillary Clinton during her tenure as secretary of state,” as Politico reports.

Some of Mr. Blumenthal’s exchanges with Secretary Clinton were publicly released, in the process exposing her questionable use of personal e-mail to conduct state business. It is unclear whether Clinton’s account was also breached.

The FBI is conducting a criminal investigation into whether Clinton mishandled classified information by storing it on her private e-mail server.

So far, the bureau’s review of Clinton’s server logs shows no sign of hacking, according to a source familiar with the case, says NBC.

“When Hillary Clinton says that her server is absolutely safe – you’re laughing,” said NBC reporter Cynthia McFadden during her interview with Lazar, according to a transcript released prior to the “Dateline” premiere, reports Politico.